Prior to the present invention, as shown by Heath et al., U.S. Pat. No. 3,847,867, assigned to the same assignee as the present invention and incorporated herein by reference, polyetherimides were made by effecting reaction between aromatic bis(etheranhydride) and organic diamine. These polyimides are injection-moldable high performance thermoplastics and useful in a variety of applications. Significant interest has been shown in using polyimides for manufacturing microelectronic circuit boards. Vapor phase soldering, however, has generated a need for inflexible circuit boards capable of withstanding change in shape at temperatures often exceeding the upper limits provided by available injection-moldable thermoplastics.
The present invention is based on the discovery that various aromatic bis(anhydrides), more specifically defined hereinafter, can be intercondensed with aminophenylbenzofuran amines having the formula, ##STR1## to provide polyimides having substantially enhanced glass transition temperatures and extremely limited solubility in organic solvents.